In order to optimise yield from farmed animals, in particular pigs and cattle, a number of remedies may be injected into the animal.
The term “remedy” is used herein to include any drug, medicine, remedy, or therapeutic preparation, when in a form suitable for dispensing from an applicator, or more specifically an injector, as the context requires.
Injection of the animal can be difficult, and there exists a danger that the user of the injector may be accidentally jabbed with the needle. Accidents of this type are known as “needle stick”.
In extreme cases the user may even receive an accidental dose or partial dose of the remedy. This is particularly undesirable, as some of the remedies used with this type of applicator may have significant adverse effects on the health and wellbeing of a human being.
Some injectors of the prior art attempt to reduce the risk of accidental needle stick by covering the needle of the injector with a retractable shroud. The shroud may be spring loaded so that it retracts automatically as the needle is inserted into the animal.
An additional level of safety is provided by injectors such as that described in U.S. Pat. No. 5,951,516, which discloses an applicator with a needle shroud and a trigger which must be depressed to an intermediate position before the shroud can be retracted. A trigger lock provided on the body of the injector prevents the trigger from being moved to an operational position until the shroud has been retracted by a desired amount, corresponding to a desired penetration of the needle into the animal. Only when this has occurred can the trigger be moved to the operational position and the dose injected.
The injector described in U.S. Pat. No. 5,951,516 is powered by a pressurised gas such as a compressed air or liquid petroleum gas. It would be desirable to develop an injector which had a high level of safety but which did not depend on a pressurised gas as a power source. It would also be advantageous if the safety mechanism did not depend on any sharp edge abutment, as these may be prone to wear.
Other types of applicator may also benefit from a simple and reliable mechanism which prevents doses of fluid from being dispensed accidentally, as this can cause waste of expensive product. In addition, even if a blunt application means such as a nozzle is used, it may still be desirable to shield the application means with a moveable shroud, for example if the application means is particularly delicate and easily damaged.
With injectors, a further potential source of danger to the user is the process of replacing the needle. The needle has a threaded portion with engages a complementary threaded portion provided on the outlet of the injector. The needle is provided with a formation with which a suitable tool, such as a spanner, can be engaged in order to rotate the needle and thereby engage or disengage the needle with the outlet.
The injectors of the prior art may require the needle shroud, if provided, to be retracted or removed during this process, leaving the sharp end of the needle exposed.